Printed products such as newspapers, journals, brochures, etc. often consist of a plurality of different printed components, e.g. a plurality of printed sheets, which are brought together by collecting, insertion or collation and are then e.g. sewn or stitched together or combined by an adhesive binding. For producing such printed products in high performance processes collecting, inserting and collating drums or corresponding sections are known for the purpose of collecting, inserting and/or collating. During collecting saddle-shaped supports and during inserting and collating V-shaped compartments are continuously directed past a plurality of addition points and at each addition point a further component, e.g. a further sheet is added to the product in production, whereby collecting starts with the innermost, folded sheet, inserting with the outermost, folded sheet and collating with a first, usually unfolded component. The collecting, insertion and collating processes can also be combined. With the known high performance equipment it is possible to achieve outputs of up to approximately 40,000 products per hour.
On the known equipment for combining different printed components to form a product, the formed product is usually controlled by a thickness measurement. This thickness measurement establishes whether the formed product thickness corresponds to a nominal thickness or whether it diverges from the latter. Products with thicknesses diverging from the nominal thickness are identified as defective and correspondingly dealt with, assuming that they contain the individual components in excessive numbers when too thick and that components are missing if too thin. In certain circumstances when using this control method products in which simultaneously components occur several times, whereas others are missing, can be interpreted as being fault-free. As the thickness of the individual components, e.g. sheets, is subject to a dispersion, in particular for products having a large number of components, it can also occur that the sum of said dispersions brings about a divergence of the product thickness from the nominal thickness, which is of the same order of magnitude as the thickness of the individual components, so that actually faultless products can be identified as faulty. It is not possible with the described method to identify as faulty, products which contain incorrectly printed components or incorrectly oriented components. In other words the thickness measurement on the finished product is a fault or defect control which is only effective to a very limited extent.
For controlling the homogeneity of individual components, particularly sheets, optical/electronic methods are also known. For example, EP-A1-534115 (Grapha Holding) proposes directing each sheet over a read head and reading the printing sample of a given area of each sheet during this movement, e.g. in the same way as bar codes are read. The printing sample read is then compared with a nominal sample and a fault signal generated in the case of variations. The read head is e.g. so fitted to a feeder, that on removing from the magazine of the feeder each sheet is passed over the read head. By corresponding synchronization of the removal movement and the reading function it is ensured that the same area is read on each sheet removed. Slight differences in the position of the individual sheet with respect to the read head can be interpreted as such by the software and eliminated from the evaluation process, if during the comparison of the read sample and the nominal sample the two samples to be compared are mutually displaced within certain limits until a maximum coincidence is found.
For a control method using a read head, as described hereinbefore, the individual sheets must be moved over said read head in a direction parallel to their main aces or surfaces. If the processing, such as e.g. in the described use, the removal from the magazine of a feeder incorporates such a movement, then the control method is advantageous. However, if the sheets (components of the product to be produced) only have to be moved in the described way for carrying out the control, the control method with the read head as described above, becomes complicated and costly. In the aforementioned process for producing printed products by joining individual printed components in a collecting, inserting and/or collating process it would be conceivable to have feeders with read heads in the vicinity of the different supplies. This would make it possible to detect and correct incorrect components, components with the incorrect orientation and in certain circumstances missing components in the component supply flows necessary for producing the product, but not faults and errors occurring between the supply and the collecting/inserting/collating device or during product production.
As in a gathering area corresponding to the aforementioned high performance processes, i.e. where components are added to products being produced, both the resulting products and the supplied components are conveyed with the main surfaces oriented substantially transversely (not parallel) to the conveying direction, an alternative or additional movement would have to be performed for a control with a read head as described above.